1. Field of the Invention
This invention relates to methods and apparatus for accessing databases, particularly databases having database records including image data.
2. Description of the Prior Art
When a database is accessed, a typical arrangement is that a "query" or search statement is passed to the database, and in response the database returns details of any "hits"--i.e. those database entries or records matching the criteria specified in that query.
Some databases have records containing image data. An example is a video archiving database, where single images or "picture stamps" characterising the whole of an archived video clip can be stored in a database alongside textual comments and keywords relating to that clip. When the database responds to a user query, the user can be presented with a scrollable display of the images and the textual information, enabling the user to identify a desired database record quickly.
However, when the database records contain image data, this response from the database can represent a large amount of data to be transferred to the client application or client computer making the query. This is because digitised images generally contain a large amount of data in comparison to textual information.
This large amount of data to be transferred can be acceptable when the querying application and the database are resident on the same host computer, but when they are resident on separate machines linked, for example, by a bandwidth-limited network connection such as an ethernet link, transferring such large amounts of data can become a problem. The problem is made worse in situations where the database can be accessed by multiple client computers, or in which the network is already heavily loaded with other data traffic.
One apparent way of alleviating this problem of slow transfer of the digitised images would be to compress those images using a compression technique such as the known JPEG technique. However, any delay in transferring the images to the client making the database query is then added to by the time required to decompress the images before they can be displayed. In the scrolling system described above, such delays can be subjectively very disturbing to the user.